Adaptively modulated multi-state inverter system and modulating method thereof

ABSTRACT

The present invention provides an adaptively modulated multi-state inverter system, comprising: a split capacitor, four bridge arms and an isolation switch group, on each of the four bridge arms a pair of complementary power switch groups is arranged; the isolation switch group comprises four fuses and six bidirectional thyristors. The output branches of the first bridge arm, the second bridge arm and the third bridge arm are respectively connected in series with a fuse to output a three-phase voltage, and at three-phase output voltage side two shared auxiliary branches are arranged, one auxiliary branch starts from the fourth bridge arm output branch on which a fuse is connected in series and is then connected to the output terminal of the three-phase voltage via three bidirectional thyristors. The other auxiliary branch starts from the DC side feed branch from the midpoint of the split capacitor, and is connected with the output terminal of the three-phase voltage via three bidirectional thyristors respectively. The invention also provides a modulating method of the multi-state inverter system. The use of the adaptive modulating technology enables the multi-state inverter to have the functions of overcurrent protection, isolation of faulty bridge arms and fault-tolerant control on any single and double bridges.

CROSS-REFERENCE TO RELATED APPLICATIONS

The subject application claims priority of the Chinese inventionapplication 202010839042.X filed on Aug. 19, 2020 in China. The contentsand subject matter thereof are incorporated herein by reference.

FIELD OF INVENTION

The present invention relates to the field of power electronics, inparticular to an adaptively modulated multi-state inverter system and amodulating method thereof.

BACKGROUND ART

As the core component for energy conversion, an inverter's performancedirectly relates to the efficiency and reliability of the energyconversion. However, due to the fragility of the power electronicdevices in the inverter, system failures occur frequently, whichdirectly cause economic losses in industrial production, and causecatastrophic accidents in important places such as aerospace, subways,and electric vehicles.

In the traditional fault-tolerant inverter, only the failure of thesingle and double power switches can be solved at most; this makes thefault-tolerant inverter to withstand fewer types of faults at this stageand somewhat limits the reliability of inverter system. However, thelocation and the number of the occurred faults in the inverter are atrandom, and we need to find an inverter strain system to adapt to andwithstand multiple types of faults.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an adaptivelymodulated multi-state inverter system and a modulating method thereof tosolve the problem that the current fault-tolerant inverter can withstandfewer types of faults.

To solve the above technical problems, the technical solution of thepresent invention is to provide an adaptively modulated multi-stateinverter system, including: a split capacitor; a first bridge arm, asecond bridge arm, a third bridge arm and a fourth bridge arm; and anisolation switch;

wherein on each of the first, second and third bridge arms a pair ofcomplementary power switch groups is arranged;

wherein the isolation switch group comprises a first fuse, a secondfuse, a third fuse and a fourth fuse as well as a first bidirectionalthyristor, a second bidirectional thyristor, a third bidirectionalthyristor, a fourth bidirectional thyristor, a fifth bidirectionalthyristor and a sixth bidirectional thyristor;

on each output branch of the first bridge arm, the second bridge arm,and the third bridge arm, a corresponding one of the first fuse, thesecond fuse and the third fuse is connected in series such that theoutput branches of the first, second and third bridge arms output athree-phase voltage, and at the three-phase output voltage side a firstshared auxiliary branch and a second shared auxiliary branch arearranged;

the first auxiliary branch starts from an output branch of the fourthbridge arm, on which output branch the fourth fuse is connected and isthen connected to an output terminal of the three-phase voltage via thefirst, second and third bidirectional thyristors;

the second auxiliary branches starts from the DC side feed branch fromthe midpoint of the split capacitor, and is connected to the outputterminal of the three-phase voltage via the fourth, fifth, and sixthbidirectional thyristors respectively.

The present invention also provides a modulating method of theadaptively modulated multi-state inverter system, which includes thefollowing steps:

step A. Monitoring the four fuses in the isolation switch group in realtime to obtain the number of faulty bridge arms, determining a faultybridge arm matrix according to the number of faulty bridge arms;

step B. According to the number of faulty bridge arms, locating thefaulty bridge arms and outputting the working state factor S; when thenumber of faulty bridge arms in the faulty bridge arm matrix is 0, S=1;when the number of faulty bridge arms in the faulty bridge arm matrix is1, S=2; and when the number of faulty bridge arms in the faulty bridgearm matrix is 2, S=3;

step C. Calculating conduction time of the power switch in the sector Nt_(SN)=[t₁ t₂ t₀] for S, wherein t₁ denoting a first vector action time,t₂ denoting a second vector action time and t₀ denoting a zero vectoraction time: When the working state factor S≤2, a six-switchfault-tolerant modulating algorithm is adopted, the six-switchfault-tolerant modulating algorithm comprises following steps:

step 11. in the stationary coordinate system α−β, calculating a targetoutput voltage of the inverter:

U _(ref) ∠θ=U _(α) +jU _(β),

wherein U_(α) and U_(β) are the components of the target voltage on axisα and β respectively;

step 12. calculating the angle θ₁ between sector I and sector N in whichsector the target voltage is in three-phase six-switch operating spacevector diagram:

$\left\{ {\begin{matrix}{{N = \ {{ceil}\ \left( \frac{\theta}{\pi/3} \right)}}\ } \\{{\theta_{1} = \ {re{m\ \left( \frac{\theta}{\pi/3} \right)}}}\ }\end{matrix};} \right.$

step 13. calculating a working state S_(N) of the power switch in thesector N:

$\begin{matrix}{S_{N} = \begin{bmatrix}S_{AN} & S_{BN} & S_{CN} & S_{XN}\end{bmatrix}} \\{= \left\{ {\begin{matrix}{{S_{I}\Lambda_{1}^{\frac{N - 1}{2}}\Lambda_{a}},{N = I},{III},V} \\{{S_{I}\Lambda_{2}\Lambda_{1}^{\frac{N}{2} - 1}\Lambda_{a}},{N = {II}},{IV},{VI}}\end{matrix},} \right.}\end{matrix}$ wherein ${\Lambda_{1} = \begin{bmatrix}0 & 1 & 0 & 0 \\0 & 0 & 1 & 0 \\1 & 0 & 0 & 0 \\0 & 0 & 0 & 1\end{bmatrix}},\mspace{11mu}{\Lambda_{2} = \begin{bmatrix}0 & 1 & 0 & 0 \\1 & 0 & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & 1\end{bmatrix}},{\Lambda_{a}\;\begin{bmatrix}a_{11} & 0 & 0 & a_{14} \\0 & a_{22} & 0 & a_{24} \\0 & 0 & a_{33} & a_{34} \\0 & 0 & 0 & 0\end{bmatrix}},$

wherein Λ_(a) is defined as the fault signal matrix for no fault orsingle bridge arm fault in the six-switch fault-tolerant modulatingalgorithm, and the elements a_(ij) in Λ_(a) depend on the working stateof the inverter. when the inverter has no fault, the fault signala_(ii)=1, a_(i4)=0; when a single bridge arm, gth bridge arm fails inthe converter, and the hth, kth and fourth bridge arms are redundant andfault-free bridge arms, then the fault signal a_(gg)=a_(h4)=a_(k4)=0,a_(gg)=a_(hh)=a_(kk)=1;

step 14. calculating conduction time of the power switch in the sector Nas follows:

when S=1, determining the first vector action time t₁, the second vectoraction time t₂ and the zero vector action time t₀ as follows:

$\left\{ {\begin{matrix}{t_{1} = {\sqrt{3}\frac{U_{ref}}{U_{dc}}T_{S}{\sin\left( {\frac{\pi}{3} - \theta_{1}} \right)}}} \\{t_{2} = {\sqrt{3}\frac{U_{ref}}{U_{dc}}T_{S}\sin\theta_{1}}} \\{t_{0} = {\frac{1}{2}\left( {T_{S} - t_{1} - t_{2}} \right)}}\end{matrix},} \right.$

the conduction time of the power switch in the sector N is determined bythe following equation:

t_(SN) = t_(SI)Λ₃^(N − 1), wherein ${\Lambda_{3} = \begin{bmatrix}0 & 1 & 0 \\1 & 0 & 0 \\0 & 0 & 1\end{bmatrix}};$

When the working state factor S=3, a four-switch fault-tolerantmodulating algorithm is adopted, the four-switch fault-tolerantmodulating algorithm comprises following steps:

step 21. calculating position N of the target voltage U_(ref)∠θ in thefour-switch operating space vector sector:

${N = {{ceil}\left( \frac{\theta}{\pi/2} \right)}};$

step 22. calculating an acute angle θ₂ between the target voltageU_(ref)∠θ and the axis α:

$\theta_{2} = \left\{ {\begin{matrix}{{re{m\ \left( \frac{\theta}{\pi/2} \right)}}\ ,\ {N = 1},3} \\{{\frac{\pi}{2} - \ {re{m\ \left( \frac{\theta}{\pi/2} \right)}}}\ ,\ {N = 2},4}\end{matrix};} \right.$

step 23. calculating the four-leg switch sequence as follows: when S=1the working state of the power switch in the sector I is known to beS_(I)=[S_(AI) S_(BI) S_(CI) S_(XI)] respectively, and the working stateof the power switch in the sector N when S=3 can be calculated from thefollowing equation:

$\begin{matrix}{S_{N} = \begin{bmatrix}S_{AN} & S_{BN} & S_{CN} & S_{XN}\end{bmatrix}} \\{= \left\{ {\begin{matrix}{{S_{I}\Lambda_{5}\Lambda_{4}^{N - 1}\Lambda_{b}},{N = 1},4} \\{{S_{I}\Lambda_{6}\Lambda_{4}^{N - 2}\Lambda_{b}},{N = 2},3}\end{matrix},} \right.}\end{matrix}$ wherein ${\Lambda_{4} = \begin{bmatrix}0 & 1 & 0 & 0 \\0 & 0 & 1 & 0 \\1 & 0 & 0 & 0 \\0 & 0 & 0 & 1\end{bmatrix}},\mspace{14mu}{\Lambda_{5} = \begin{bmatrix}0 & 0 & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & 1 \\0 & 0 & 0 & 0\end{bmatrix}},\mspace{14mu}{\Lambda_{6} = \begin{bmatrix}0 & 0 & 1 & 0 \\0 & 0 & 0 & 1 \\0 & 0 & 0 & 0 \\0 & 0 & 0 & 0\end{bmatrix}},{\Lambda_{b} = \begin{bmatrix}0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 \\b_{31} & b_{32} & b_{33} & b_{34} \\b_{41} & b_{42} & b_{43} & b_{44}\end{bmatrix}},$

wherein Λ_(b) being a healthy signal matrix in the four-switchfault-tolerant modulating algorithm, its elements b_(ij) and a_(ij)depend on the working state of the inverter; when S=3 and a doublebridge arm failure occurs in the inverter and only the 1st and the mthbridge arms are fault-free bridge arms and m>l, there is a healthysignal b_(3l)=1, b_(4m)=1; other elements b_(ij) are all 0;

step 24. calculating conduction time of each switching o in the sector Nas follows:

the conduction time of each switching of the four bridge arms can beexpressed as t_(SN)=[t₁ t₂ t₀], the first vector action time t₁, thesecond vector action time t₂ and the zero vector action time t₀ can bedetermined by the following equation:

$\left\{ {\begin{matrix}{t_{1} = {3\frac{U_{ref}}{U_{dc}}T_{S}{\sin\left( {\frac{\pi}{2} - \theta_{2}} \right)}}} \\{t_{2} = {\sqrt{3}\frac{U_{ref}}{U_{dc}}T_{S}\sin\theta_{2}}} \\{t_{0} = {\frac{1}{2}\left( {T_{S} - t_{1} - t_{2}} \right)}}\end{matrix};} \right.$

The adaptively modulated multi-state inverter system provided by thepresent invention incorporates a multi-state inverter and uses adaptivemodulating technology to make the multi-state inverter to have thefunction of overcurrent protection, isolation of faulty bridge arm andfault-tolerant control on any single or double bridge arms; there aremany types of faults that can be withstood, including not only singleswitch failure, double switch failures, but also three switch failuresand four switch failures; after any single bridge arm failure occurs andsuccessful fault-tolerant is achieved, the function of fault-tolerantcontrol can still be realized even if the single bridge arm failureoccurs again and further leads to a successive double bridge armfailures.

The modulating method of an adaptively modulated multi-state invertersystem of the present invention is a space vector modulating technologybased on adaptive controlment, which can flexibly modulate healthybridge arms according to the specific working state factors of themulti-state inverter. First of all, it is necessary to monitor theworking state of the fuse in real time. When any single or double bridgearms fails, the fuse on the corresponding faulty phase will beautomatically blown to activate the function of isolating the faultybridge arm and determine the faulty bridge arm matrix, so as todetermine the working state factor according to the number of faultybridge arms; finally, the function of modulating healthy bridge arms isrealized by the working state factor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic circuit diagram of an adaptive modulatedmulti-state inverter system in one embodiment of the present invention;

FIG. 2 is a flowchart of the steps of a modulating method of theadaptive modulated multi-state inverter system of the present invention;

FIG. 3 is a space vector diagram of a multi-state fault-tolerantinverter when S 2 in one embodiment of the present invention;

FIG. 4a is a switching sequence diagram in the sector I of themulti-state fault-tolerant inverter with no fault and when S≤2 in oneembodiment of the present invention;

FIG. 4b is a switching sequence diagram in the sector II of multi-statefault-tolerant inverter the with fault in phase A and when S≤2 in oneembodiment of the present invention;

FIG. 5 is a space vector diagram of a multi-state fault-tolerantinverter when S=3 in one embodiment of the present invention;

FIG. 6a is a switching sequence diagram in the sector I of themulti-state fault-tolerant inverter with fault in phases A&B and whenS=3 in one embodiment of the present invention;

FIG. 6b is a switching sequence diagram in the sector II of themulti-state fault-tolerant inverter with fault in phases A&B and whenS=3 in one embodiment of the present invention.

EMBODIMENTS

In the following, an adaptive modulated multi-state inverter system andits modulating method of the present invention will be further describedin detail with reference to the accompanying drawings and specificembodiments. According to the following description and claims, theadvantages and features of the present invention will be clearer. Itshould be noted that the drawings are in a very simplified form and useimprecise ratios, which are only used to conveniently and clearly assistin explaining the purpose of the embodiments of the present invention.

FIG. 1 is a schematic circuit diagram of an adaptive modulatedmulti-state inverter system in one embodiment of the present invention.Referring to FIG. 1, an adaptively modulated multi-state inverter systemis provided, including: a split capacitor 11; four bridge arms, each hasa pair of complementary power switch groups; an isolation switch group13, including four fuses and six bidirectional thyristors. The fusesF_(a), F_(b), F_(c) are respectively connected in series on the outputbranches of the first bridge arm 121, the second bridge arm 122, and thethird bridge arm 123 which output a three-phase voltage, and at thethree-phase output voltage side two shared auxiliary branches arearranged, one of the auxiliary branches starts from the output branch ofthe fourth bridge arm 124, on which output branch a fuse F_(x) isconnected, and is then connected to the output terminal of thethree-phase voltage via three bidirectional thyristors TR_(a1), TR_(b1)and TR_(c1); the other of the auxiliary branches states from the DC sidefeed branch drawn from the midpoint of the split capacitor, and isdirectly connected to the output terminal of the three-phase voltage viathree bidirectional thyristors TR_(a2), TR_(b2) and TR_(c2)respectively.

To facilitate describing the technical solution, in the embodiment ofthe present invention, the first bridge arm is named bridge arm A,comprising the power switch group IGBT1, IGBT2, the second bridge arm isnamed bridge arm B, comprising the power switch group IGBT3, IGBT4, andthe third bridge arm is named bridge arm C, comprising the power switchgroup IGBT5, IGBT6, and the fourth bridge arm is named bridge arm X,comprising the power switch group IGBT7, IGBT8.

The adaptively modulated multi-state inverter system can withstand anysingle or double-arm failure. Table 1 is a list of the types of failuresthat an adaptively modulated multi-state inverter system can withstand.Referring to Table 1, the embodiment of the present invention mainlyincludes 36 types of switch faults, including not only 6 single switchfaults, 15 double switch faults, but also 12 types of three switchfaults and 3 types of four switch faults.

TABLE 1 Number of Number of fault Faulty bridge fault bridge switchesFault switch arm arm single switch IGBT1 fault bridge arm A single faultIGBT2 fault bridge arm A bridge IGBT3 fault bridge arm B arm fault IGBT4fault bridge arm B IGBT5 fault bridge arm C IGBT6 fault bridge arm Cdouble switch IGBT1 

 2 fault bridge arm A faults IGBT3 

 4 fault bridge arm B IGBT5 

 6 fault bridge arm C IGBT1 

 3 fault bridge arms double A&B bridge IGBT1 

 4 fault bridge arms arm fault A&B IGBT2 

 3 fault bridge arms A&B IGBT2 

 4 fault bridge arms A&B IGBT3 

 5 fault bridge arms B&C IGBT3 

 6 fault bridge arms B&C IGBT4 

 5 fault bridge arms B&C IGBT4 

 6 fault bridge arms B&C IGBT5 

 1 fault bridge arms C&A IGBT5 

 2 fault bridge arms C&A IGBT6 

 1 fault bridge arms C&A IGBT6 

 2 fault bridge arms C&A three switch IGBT1 

 2 

 3 bridge arms faults fault A&B IGBT1 

 2 

 4 bridge arms fault A&B IGBT1 

 3 

 4 bridge arms fault A&B IGBT2 

 3 

 4 bridge arms fault A&B IGBT3 

 4 

 5 bridge arms fault B&C IGBT3 

 4 

 6 bridge arms fault B&C IGBT3 

 5 

 6 bridge arms fault B&C IGBT4 

 5 

 6 bridge arms fault B&C IGBT5 

 6 

 1 bridge arms fault C&A IGBT5 

 6 

 2 bridge arms fault C&A IGBT5 

 1 

 2 bridge arms fault C&A IGBT6 

 1 

 2 bridge arms fault C&A four switch IGBT1 

 2 

 3 

 4 fault bridge arms faults A&B IGBT3 

 4 

 5 

 6 fault bridge arms B&C IGBT5 

 6 

 1 

 2 fault bridge arms C&A

FIG. 2 is the flowchart of the steps of a modulating method of anadaptively modulated multi-state inverter system of the presentinvention. Referring to FIG. 2, the present invention also provides amodulating method of an adaptively modulated multi-state invertersystem, which includes the following steps:

step A: Monitoring the working state of the four fuses in the isolationswitch group in real time, determining the state factors of the fourfuses, and determining the faulty bridge arm matrix according to thestate factors;

step B: According to the number of faulty bridge arms in the faultybridge arm matrix, locating the faulty bridge arm and outputting theworking state factor S;

step C: When the number of faulty bridge arms in the faulty bridge armmatrix is 0, S=1; when the number of faulty bridge arms in the faultybridge arm matrix is 1, S=2; when the number of faulty bridge arms inthe faulty bridge arm matrix is 2, S=3; when the working state factorS≤3, a six-switch fault-tolerant modulating algorithm is adopted; andwhen the working state factor S=3, a four-switch fault-tolerantmodulating algorithm is adopted.

Specifically in step A, the working state of the four fuses F_(a),F_(b), F_(c) and F_(x) in the isolation switch group is monitored inreal time, and the state factors of the four fuses f_(a), f_(b), f_(c)and f_(x) is determined, and also the faulty bridge arm matrix F=[f_(a)f_(b) f_(c) f_(x)] is determined. Specifically, when the fuse is workingnormally, its state factor is set to be 0, and when the fuse is blowndue to an overcurrent caused by a faulty bridge arm, its state factor isset to be 1.

The failure of any bridge arm in the inverter will generate anovercurrent, which will make a corresponding fuse (F_(a), F_(b), F_(c)or F_(x)) in the isolation switch group to automatically blow due to theheat generated by itself. In this way, the function of isolating thefaulty bridge arm is automatically activated, and the entire system isprotected from further damage caused by the faulty bridge arm.

Based on the number of faulty bridge arms in the faulty bridge armmatrix F, the faulty bridge arms can be located, thereby thecorresponding optimal working state can be determined, and the workingstate factor S can be output.

Table 2 is a classification of fault-tolerant working state. Referringto Table 2, when the number of faulty bridge arms in the faulty bridgearm matrix F is 0, S=1; when the number of faulty bridge arms in thefaulty bridge arm matrix F is 1, S=2; and when the number of faultybridge arms in the faulty bridge arm matrix F is 2, S=3.

TABLE 2 faulty bridge arm matrix F faulty bridge arm working statefactor S [0 0 0 0] — 1 [1 0 0 0] bridge arm A 2 [0 1 0 0] bridge arm B 2[0 0 1 0] bridge arm C 2 [1 1 0 0] bridge arms A&B 3 [0 1 1 0] bridgearms B&C 3 [1 0 1 0] bridge arms C&A 3 [1 0 0 1] bridge arms A&X 3 [0 10 1] bridge arms B&X 3 [0 0 1 1] bridge arms C&X 3

When the working state factor S≤2, the six-switch fault-tolerantmodulating algorithm is adopted, specifically as follows:

In the space vector modulating algorithm based on sector conversion, thesix-switch fault-tolerant modulating algorithm can be used for themulti-state fault-tolerant inverter when S=1 or S=2. FIG. 3 is a spacevector diagram of a multi-state fault-tolerant inverter when S≤2 in oneembodiment of the present invention. Referring to FIG. 3, in thestationary coordinate system α−β, the target output voltage of theinverter should be:

U _(ref) ∠θ=U _(α) +jU _(β)  (1)

wherein U_(α) and U_(β) are the components of the target voltage on axisα and β respectively.

In the stationary coordinate system α−β, the sector N in the three-phasesix-switch operating space vector diagram can be determined according tothe angle θ of the target voltage U_(ref)∠θ. In addition, the remaindercalculation of θ will be performed to convert the target voltage to thesector I and obtain the angle θ₁ of the sector I as shown in FIG. 3.

$\begin{matrix}\left\{ \begin{matrix}{N = {{ceil}\left( \frac{\theta}{\pi\text{/}3} \right)}} \\{\theta_{1} = {{rem}\left( \frac{\theta}{\pi\text{/}3} \right)}}\end{matrix} \right. & (2)\end{matrix}$

FIG. 4a is a switching sequence diagram in the sector I when themulti-state fault-tolerant inverter with no fault and S≤2 in oneembodiment of the present invention. Referring to FIG. 4a , the workingstate of the power switch in the sector I is S_(I)=[S_(AI) S_(BI) S_(CI)S_(XI)] when S=1. The specific switching sequence is exemplified by theseven-segment type as shown in FIG. 4a . When S≤2, the working stateS_(N) of the power switch in the sector N can be obtained by thefollowing equation:

$\begin{matrix}{\mspace{76mu}{\begin{matrix}{S_{N} = \left\lbrack {S_{AN}\mspace{14mu} S_{BN}\mspace{14mu} S_{CN}\mspace{14mu} S_{XN}} \right\rbrack} \\{= \left\{ \begin{matrix}{{{S_{1}\Lambda_{1}^{\frac{N - 1}{2}}\Lambda_{a}},{N = I},{III},V}\mspace{45mu}} \\{{S_{1}\Lambda_{2}\Lambda_{1}^{\frac{N}{2} - 1}\Lambda_{a}},{N = {II}},{IV},{VI}}\end{matrix} \right.}\end{matrix}{{{{wherein}\mspace{14mu}\Lambda_{1}} = \begin{bmatrix}0 & 1 & 0 & 0 \\0 & 0 & 1 & 0 \\1 & 0 & 0 & 0 \\0 & 0 & 0 & 1\end{bmatrix}},{\Lambda_{2} = \begin{bmatrix}0 & 1 & 0 & 0 \\1 & 0 & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & 1\end{bmatrix}},{\Lambda_{a} = {\begin{bmatrix}a_{11} & 0 & 0 & a_{14} \\0 & a_{22} & 0 & a_{24} \\0 & 0 & a_{33} & a_{34} \\0 & 0 & 0 & 0\end{bmatrix}.}}}}} & (3)\end{matrix}$

Λ_(a) is defined as the fault signal matrix for no fault (S=1) or singlebridge arm fault (S=2) in the six-switch fault-tolerant modulatingalgorithm, and the elements a_(ij) in Λ_(a) depend on the working stateof the inverter. When the inverter has no fault (S=1), the fault signala_(ii)=1, a_(i4)=0; when a single bridge arm, gth bridge arm, fails, ahth and a kth bridge arm are fault-free and the fourth bridge arm isredundant, then the fault signal a_(gg)=a_(h4)=a_(k4)=0,a_(gg)=a_(hh)=a_(kk)=1; wherein the gth, hth and kth bridge arm is oneof the first, second, and third bridge arm respectively;

Now calculate the conduction time of the power switch in the sector N.Specifically, the conduction time of the power switch in the sector I ist_(SI)=[t₁ t₂ t₀] when s=1, the first vector action time t₁, the secondvector action time t₂ and the zero vector action time t₀ are determinedby the following equation:

$\begin{matrix}\left\{ \begin{matrix}{t_{1} = {\sqrt{3}\frac{U_{ref}}{U_{dc}}T_{S}\mspace{14mu}\sin\mspace{14mu}\left( {\frac{\pi}{3} - \theta_{1}} \right)}} \\{{t_{2} = {\sqrt{3}\frac{U_{ref}}{U_{dc}}T_{S}\mspace{14mu}\sin\mspace{14mu}\theta_{1}}}\mspace{65mu}} \\{{t_{0} = {\frac{1}{2}\left( {T_{S} - t_{1} - t_{2}} \right)}}\mspace{101mu}}\end{matrix} \right. & (4)\end{matrix}$

In the case of no failure or single bridge arm failure, the conductiontime of the power switch in the sector N is determined by the followingfactors:

$\begin{matrix}{{t_{SN} = {t_{SI}\Lambda_{3}^{N - 1}}}{{{wherein}\mspace{14mu}\Lambda_{3}} = {\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 0 \\0 & 0 & 1\end{bmatrix}.}}} & (5)\end{matrix}$

The proposed six-switch fault-tolerant modulating algorithm adopts thescheme of directly outputting the PWM pulse signal. From theseven-segment switching sequence of the ABCX phase in the sector I whenS=1, the seven-segment switching sequence in the other sectors under thenormal and single-arm faults can be obtained, which indirectlydetermines the order of action of each voltage vector. FIG. 4b providesa switching sequence diagram in the sector II when the multi-statefault-tolerant inverter with fault in phase A and S≤2. When a phase Asingle-bridge-arm failure occurs in the inverter, the working statefactor S=2. Then when in the second sector N=II, the switching sequenceof the voltage vector of the four bridge arms can be calculated from theequation (3), as shown in FIG. 4 b.

When the working state factor S=3, a four-switch fault-tolerantmodulating algorithm is adopted.

FIG. 5 is a space vector diagram of a multi-state fault-tolerantinverter when S=3 in one embodiment of the present invention. Referringto FIG. 5, when S=3, it is needed to switch to the four-switchfault-tolerant modulating algorithm, no matter the target voltageU_(ref)∠θ is located in any sector, which can be determined byrecombining the relevant parameters of the S_(I) in the sector I of thethree-phase six-switch operating space vector diagram when S=1 in FIG.3.

The position of the target voltage U_(ref)∠θ in the four-switchoperating space vector sector is:

$\begin{matrix}{N = {{ceil}\left( \frac{\theta}{\pi\text{/}2} \right)}} & (6)\end{matrix}$

θ₂ shown in FIG. 5 is defined as the acute angle between the targetvoltage U_(ref)∠θ and the axis α, which is determined by the followingequation:

$\begin{matrix}{\theta_{2} = \left\{ \begin{matrix}{{{{rem}\left( \frac{\theta}{\pi\text{/}2} \right)},{N = 1},3}\mspace{50mu}} \\{{\frac{\pi}{2} - {{rem}\left( \frac{\theta}{\pi\text{/}2} \right)}},{N = 2},4}\end{matrix} \right.} & (7)\end{matrix}$

Now calculate the four-leg switch sequence as follows:

Same as above, when S=1 the working state of the power switch in thesector I is known to be S_(I)=[S_(AI) S_(BI) S_(CI) S_(XI)]respectively, and the working state of the power switch in the sector Nwhen S=3 can be calculated from the following equation.

$\begin{matrix}\begin{matrix}{S_{N} = \left\lbrack {S_{AN}\mspace{14mu} S_{BN}\mspace{14mu} S_{CN}\mspace{14mu} S_{XN}} \right\rbrack} \\{= \left\{ \begin{matrix}{{S_{I} ⩓_{5} ⩓_{4}^{N - 1} ⩓_{b}},{N = 1},4} \\{{S_{I} ⩓_{6} ⩓_{4}^{N - 2} ⩓_{b}},{N = 2},3}\end{matrix} \right.}\end{matrix} & (8) \\{{{{{{wherein}\mspace{14mu} ⩓_{4}} = \begin{bmatrix}1 & 0 & 0 & 0 \\0 & 1 & 0 & 0 \\0 & 0 & 0 & 1 \\0 & 0 & 1 & 0\end{bmatrix}},\mspace{14mu}{⩓_{5}{= \begin{bmatrix}0 & 0 & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & 1 \\0 & 0 & 0 & 0\end{bmatrix}}},\mspace{14mu}{⩓_{6} =}}\quad}{\quad{\quad{\left\lbrack {\quad\begin{matrix}0 & 0 & 1 & 0 \\0 & 0 & 0 & 1 \\0 & 0 & 0 & 0 \\0 & 0 & 0 & 0\end{matrix}\quad} \right\rbrack,\mspace{14mu}{⩓_{b}{= {\begin{bmatrix}0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 \\b_{31} & b_{32} & b_{33} & b_{34} \\b_{41} & b_{42} & b_{43} & b_{44}\end{bmatrix}.}}}}}}} & \;\end{matrix}$

Λ_(b) being a healthy signal matrix in the four-switch fault-tolerantmodulating algorithm, its elements b_(ij) and a_(ij) also depend on theworking state of the inverter. When S=3, which means a double bridge armfailure occurs in the inverter, only the 1st and the mth bridge arms arefault-free bridge arms and m>1, there is a healthy signal b_(3l)=1,b_(4m)=1; other elements b_(ij) are all 0.

Now calculate conduction time in the sector N as follows:

The conduction time of each switching of the four bridge arms can beexpressed as t_(SN)=[t₁ t₂ t₀], which means each sector has the sameconduction time of each switching. The first vector action time t₁, thesecond vector action time t₂ and the zero vector action time t₀ can alsobe determined by the following equation:

$\begin{matrix}\left\{ \begin{matrix}{{t_{1} = {3\frac{U_{ref}}{U_{dc}}T_{S}\mspace{14mu}\sin\mspace{14mu}\left( {\frac{\pi}{2} - \theta_{2}} \right)}}\mspace{20mu}} \\{{t_{2} = {\sqrt{3}\frac{U_{ref}}{U_{dc}}T_{S}\mspace{14mu}\sin\mspace{14mu}\theta_{2}}}\mspace{65mu}} \\{{t_{0} = {\frac{1}{2}\left( {T_{S} - t_{1} - t_{2}} \right)}}\mspace{101mu}}\end{matrix} \right. & (9)\end{matrix}$

The proposed four-switch fault-tolerant modulating algorithm adopts thescheme of directly outputting the PWM pulse signal. From the seven-stageswitching sequence of phases A, B, C and X in the sector I (as shown inFIG. 4a ) when S=1, the seven-segment switching sequence in othersectors under other working conditions can be obtained for double bridgearm failure when S=3, thereby the order of action of each voltage vectorcan be indirectly determined. FIG. 6a is a switching sequence diagram inthe sector I in the embodiment of the present invention when the A&Bphases of the multi-state fault-tolerant inverter fails which means S=3;FIG. 6b is a switching sequence diagram in the sector II in theembodiment of the present invention when the A&B phases of themulti-state fault-tolerant inverter fails which means S=3. Referring toFIG. 6a and FIG. 6b , when the inverter is in the state of A&Bdouble-bridge-arm fault which means S=3, according to the aboveequations, the switching sequence in the sector I and the sector II canbe obtained.

Obviously, those skilled in the art are capable of making variouschanges and modifications to the present invention without departingfrom the spirit and scope of the present invention, which shall fallwithin the scope of the claims of the present invention.

1. An adaptively modulated multi-state inverter system, comprising: asplit capacitor, a first bridge arm, a second bridge arm, a third bridgearm, a fourth bridge arm and an isolation switch; wherein on each of thefirst, second and third bridge arms a pair of complementary power switchgroups is arranged; the isolation switch group comprises a first fuse, asecond fuse, a third fuse and a fourth fuse as well as a firstbidirectional thyristor, a second bidirectional thyristor, a thirdbidirectional thyristor, a fourth bidirectional thyristor, a fifthbidirectional thyristor and a sixth bidirectional thyristor; on eachoutput branch of the first bridge arm, the second bridge arm, and thethird bridge arm, a corresponding one of the first fuse, the second fuseand the third fuse is connected in series such that the output branchesof the first, second and third bridge arms output a three-phase voltage,and at a three-phase output voltage side a first shared auxiliary branchand a second shared auxiliary branch are arranged; the first auxiliarybranch starts from an output branch of the fourth bridge arm, on whichoutput branch the fourth fuse is connected and is then connected to anoutput terminal of the three-phase voltage via the first, second andthird bidirectional thyristors respectively; the second auxiliarybranches starts from a DC side feed branch from a midpoint of the splitcapacitor, and is connected to the output terminal of the three-phasevoltage via the fourth, fifth, and sixth bidirectional thyristorsrespectively.
 2. A modulating method of the adaptively modulatedmulti-state inverter system of claim 1, comprising the following steps:step A. monitoring the four fuses in the isolation switch group in realtime to obtain a number of faulty bridge arms, determining a faultybridge arm matrix according to the number of faulty bridge arms; step B.locating the faulty bridge arms and outputting a working state factor Saccording to the number of faulty bridge arms: setting S=1 when thenumber of faulty bridge arms in the faulty bridge arm matrix is 0;setting S=2 when the number of faulty bridge arms in the faulty bridgearm matrix is 1; setting S=3 when the number of faulty bridge arms inthe faulty bridge arm matrix is 2; step C. calculating conduction timeof the power switch in a sector N t_(SN)=[t₁ t₂ t₀] for S, wherein t₁denoting a first vector action time, t₂ denoting a second vector actiontime and t₀ denoting a zero vector action time: when the working statefactor S≤2, going to step 11, otherwise going to step 21: step
 11. in astationary coordinate system α−β, calculating a target output voltage ofthe inverter:U _(ref) ∠θ=U _(α) +jU _(β) wherein U_(α) and U_(β) are components of atarget voltage on axis α and β respectively; step
 12. calculating anangle θ₁ between a sector I and the sector N wherein the target voltageis in three-phase six-switch operating space vector diagram:$\left\{ {\begin{matrix}{N = {{ceil}\left( \frac{\theta}{\pi\text{/}3} \right)}} \\{\theta_{1} = {{rem}\left( \frac{\theta}{\pi\text{/}3} \right)}}\end{matrix};} \right.$ step
 13. calculating a working state S_(N) ofthe power switch in the sector N: $\mspace{70mu}{\begin{matrix}{S_{N} = \left\lbrack {S_{AN}\mspace{14mu} S_{BN}\mspace{14mu} S_{CN}\mspace{14mu} S_{XN}} \right\rbrack} \\{= \left\{ \begin{matrix}{{{S_{1}\Lambda_{1}^{\frac{N - 1}{2}}\Lambda_{a}},{N = I},{III},V}\mspace{45mu}} \\{{S_{1}\Lambda_{2}\Lambda_{1}^{\frac{N}{2} - 1}\Lambda_{a}},{N = {II}},{IV},{VI}}\end{matrix} \right.}\end{matrix},{{{wherein}\mspace{14mu}\Lambda_{1}} = \begin{bmatrix}0 & 1 & 0 & 0 \\0 & 0 & 1 & 0 \\1 & 0 & 0 & 0 \\0 & 0 & 0 & 1\end{bmatrix}},{\Lambda_{2} = \begin{bmatrix}0 & 1 & 0 & 0 \\1 & 0 & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & 1\end{bmatrix}},{\Lambda_{a} = \begin{bmatrix}a_{11} & 0 & 0 & a_{14} \\0 & a_{22} & 0 & a_{24} \\0 & 0 & a_{33} & a_{34} \\0 & 0 & 0 & 0\end{bmatrix}},}$ Λ_(a) denoting fault signal matrix for no fault orsingle bridge arm fault, and elements a_(ij) in Λ_(a) representingworking state of the inverter; when the inverter has no fault, settinga_(ii)=1, a_(i4)=0; when a single bridge arm, gth bridge arm, fails, anhth and a kth bridge arm are fault-free and the fourth bridge arm isredundant, setting a_(gg)=a_(h4)=a_(k4)=0, a_(gg)=a_(hh)=a_(kk)=1;wherein the gth, hth and kth bridge arm is one of the first, second, andthird bridge arm respectively; step
 14. calculating the conduction timeof the power switch in the sector N as follows: when S=1, determiningthe first vector action time t₁, the second vector action time t₂ andthe zero vector action time t₀ as follows: $\left\{ {\begin{matrix}{t_{1} = {\sqrt{3}\frac{U_{ref}}{U_{dc}}T_{S}\mspace{14mu}\sin\mspace{14mu}\left( {\frac{\pi}{3} - \theta_{1}} \right)}} \\{{t_{2} = {\sqrt{3}\frac{U_{ref}}{U_{dc}}T_{S}\mspace{14mu}\sin\mspace{14mu}\theta_{1}}}\mspace{65mu}} \\{{t_{0} = {\frac{1}{2}\left( {T_{S} - t_{1} - t_{2}} \right)}}\mspace{101mu}}\end{matrix};} \right.$ obtaining conduction time of the power switch inthe sector N as follows:${t_{SN} = {t_{SI}\Lambda_{3}^{N - 1}}},{{{{wherein}\mspace{14mu}\Lambda_{3}} = \begin{bmatrix}0 & 1 & 0 \\1 & 0 & 0 \\0 & 0 & 1\end{bmatrix}};}$ going to step D; step
 21. calculating position N ofthe target voltage U_(ref)∠θ in the four-switch operating space vectorsector: ${N = {{ceil}\left( \frac{\theta}{\pi\text{/}2} \right)}};$ step22. calculating an acute angle θ₂ between the target voltage U_(ref)∠θand the axis a: $\theta_{2} = \left\{ {\begin{matrix}{{{{rem}\left( \frac{\theta}{\pi\text{/}2} \right)},{N = 1},3}\mspace{50mu}} \\{{\frac{\pi}{2} - {{rem}\left( \frac{\theta}{\pi\text{/}2} \right)}},{N = 2},4}\end{matrix};} \right.$ step
 23. calculating a four-leg switch sequenceas follows: when S=3 with working state of the power switch in thesector I being denoted as S_(I)=[S_(AI) S_(BI) S_(CI) S_(XI)],calculating the working state of the power switch in the sector N asfollows: $\mspace{76mu}\begin{matrix}{S_{N} = \left\lbrack {S_{AN}\mspace{14mu} S_{BN}\mspace{14mu} S_{CN}\mspace{14mu} S_{XN}} \right\rbrack} \\{= \left\{ {\begin{matrix}{{S_{I}\Lambda_{5}\Lambda_{4}^{N - 1}\Lambda_{b}},{N = 1},4} \\{{S_{I}\Lambda_{6}\Lambda_{4}^{N - 2}\Lambda_{b}},{N = 2},3}\end{matrix},} \right.}\end{matrix}$ ${{{wherein}\mspace{14mu}\Lambda_{4}} = \begin{bmatrix}1 & 0 & 0 & 0 \\0 & 1 & 0 & 0 \\0 & 0 & 0 & 1 \\0 & 0 & 1 & 0\end{bmatrix}},{\Lambda_{5} = \begin{bmatrix}0 & 0 & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & 1 \\0 & 0 & 0 & 0\end{bmatrix}},{\Lambda_{6} = \begin{bmatrix}0 & 0 & 1 & 0 \\0 & 0 & 0 & 1 \\0 & 0 & 0 & 0 \\0 & 0 & 0 & 0\end{bmatrix}},{\Lambda_{b} = \begin{bmatrix}0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 \\b_{31} & b_{32} & b_{33} & b_{34} \\b_{41} & b_{42} & b_{43} & b_{44}\end{bmatrix}},$ wherein Λ_(h) being a healthy signal matrix; settingelements b_(ij) as follows: for S=3 and a double bridge arm failureoccurrence in the inverter, with a 1st and an mth bridge arms beingfault-free bridge arms and m>l, setting b_(3l)=1, b_(4m)=1; settingother elements b_(ij) to be 0; step
 24. calculating the conduction timeof the power switch in the sector N as follows: determining the firstvector action time t₁, the second vector action time t₂ and the zerovector action time t₀ by the following equation:$\left\{ {\begin{matrix}{{t_{1} = {3\frac{U_{ref}}{U_{dc}}T_{S}\mspace{14mu}\sin\mspace{14mu}\left( {\frac{\pi}{2} - \theta_{2}} \right)}}\mspace{20mu}} \\{{t_{2} = {\sqrt{3}\frac{U_{ref}}{U_{dc}}T_{S}\mspace{14mu}\sin\mspace{14mu}\theta_{2}}}\mspace{65mu}} \\{{t_{0} = {\frac{1}{2}\left( {T_{S} - t_{1} - t_{2}} \right)}}\mspace{101mu}}\end{matrix};} \right.$ obtaining conduction time of the power switch inthe sector N as follows:t _(SN)=[t ₁ t ₂ t ₀]; step D. outputting PWM pulse signals based on theconduction time of the power switch in the sector N to realize faulttolerance.